Table Of Contents

Computes the frequency response and the coherence and returns the results as the real and imaginary parts of the averaged frequency response.

This node calculates the frequency response of the channels in the stimulus signal against the channels in the response signal according to the following table:

Stimulus Signal

Response Signal

Results

One channel

One channel

One output.

Multiple channels

One channel

The first channel in the stimulus signal against the single channel in the response signal, the second channel in the stimulus signal against the single channel in the response signal, and so on. The output contains the same number of channels as the stimulus signal.

One channel

Multiple channels

The single channel in the stimulus signal against the first channel in the response signal, the single channel in the stimulus signal against the second channel in the response signal, and so on. The output contains the same number of channels as the response signal.

window parameter

A value that affects the output coefficients when window type is Kaiser, Gaussian, or Dolph-Chebyshev.

If window type is any other type of window, this node ignores this input.

This input represents the following information for each type of window:

Kaiser—Beta parameter

Gaussian—Standard deviation

Dolph-Chebyshev—The ratio of the main lobe to the side lobe, s, expressed in decibels

Default: NaN—Causes this node to set beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 dB for a Dolph-Chebyshev window

window type

Time-domain window to apply to the signal.

Name

Value

Description

Rectangle

0

Applies a rectangle window.

Hanning

1

Applies a Hanning window.

Hamming

2

Applies a Hamming window.

Blackman-Harris

3

Applies a Blackman-Harris window.

Exact Blackman

4

Applies an Exact Blackman window.

Blackman

5

Applies a Blackman window.

Flat Top

6

Applies a Flat Top window.

4 Term B-Harris

7

Applies a 4 Term B-Harris window.

7 Term B-Harris

8

Applies a 7 Term B-Harris window.

Low Sidelobe

9

Applies a Low Sidelobe window.

Blackman Nutall

11

Applies a Blackman Nutall window.

Triangle

30

Applies a Triangle window.

Bartlett-Hanning

31

Applies a Bartlett-Hanning window.

Bohman

32

Applies a Bohman window.

Parzen

33

Applies a Parzen window.

Welch

34

Applies a Welch window.

Kaiser

60

Applies a Kaiser window.

Dolph-Chebyshev

61

Applies a Dolph-Chebyshev window.

Gaussian

62

Applies a Gaussian window.

Force

64

Applies a Force window.

Exponential

65

Applies an Exponential window.

Default: Hanning

restart averaging

A Boolean that specifies whether the node restarts the selected averaging process.

True

Restarts the averaging process.

False

Does not restart the averaging process.

When you call this node for the first time, the averaging process restarts automatically. A typical case when you restart averaging is when a major input change occurs in the middle of the averaging process.

Default: False

stimulus signal

The input, time domain signal x.

This input can be a waveform or an array of waveforms.

response signal

The input, time domain signal y.

This input can be a waveform or an array of waveforms.

averaging parameters

Settings that define how this node computes the averaging.

averaging mode

The mode this node uses to compute the averaging.

Name

Description

No averaging

Does not use averaging.

Vector averaging

Uses vector averaging.

RMS averaging

Uses RMS averaging.

Peak hold

Uses peak hold averaging.

Default: No averaging

weighting mode

Weighting mode for RMS and vector averaging.

Name

Description

Linear

Uses linear weighting.

Exponential

Uses exponential weighting.

Default: Exponential

number of averages

Number of averages to use for RMS and vector averaging.

If weighting mode is Exponential, the averaging process is continuous. If weighting mode is Linear, the averaging process stops after this node computes the specified number of averages.

Default: 10

error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error

error in contains an error

If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

FRF Mode

The mode this node uses to compute the frequency response function (FRF).

If you know that noise, which does not propagate through the system under test, infiltrates the input or output signals, you can select the method for computing the FRF to minimize the measurement error.

Name

Description

H1

Minimizes errors in the result when extraneous noise contaminates the output signal.

H2

Minimizes errors in the result when extraneous noise contaminates the input signal.

H3

When noise contaminates both the input and output signals, H1 and H2 provide the lower and upper bounds of the true frequency response of the system. In this case, select H3, the average of H1 and H2.

Default: H1

real

Real part of the averaged frequency response of the input signals.

f0

Start frequency, in Hz, of the spectrum.

df

Frequency resolution, in Hz, of the spectrum.

real

Real part of the averaged frequency response.

imaginary

Imaginary part of the averaged frequency response of the input signals.

f0

Start frequency, in Hz, of the spectrum.

df

Frequency resolution, in Hz, of the spectrum.

imaginary

Imaginary part of the averaged frequency response.

averaging done

A Boolean that indicates whether the number of averages this node completed is greater than or equal to the specified number of averages.

True

The number of averages this node completed is greater than or equal to the specified number of averages.

False

The number of averages this node completed is less than the specified number of averages.

averaging done is True if averaging mode is No averaging.

averages completed

Number of averages this node completed.

error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error

error in contains an error

If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

coherence

Coherence of the averaged frequency response of the input signals.

f0

Start frequency, in Hz, of the spectrum.

df

Frequency resolution, in Hz, of the spectrum.

coherence

Coherence of the averaged frequency response.

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported

Web Server: Not supported in VIs that run in a web application

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